1. Field of the Invention
The present invention relates to method and apparatus for providing spin-polarized medical-grade xenon.sup.129 gas. That is, the spin-polarized xenon.sup.129 gas provided by the present invention is of sufficient purity for use as a medical-grade contrast media in carrying out magnetic resonance imaging (MRI) procedures of lung and bronchial structures within a living human during which the living human inhales the xenon gas. The living human inhales a gas mixture including spin-polarized xenon.sup.129 gas during a MRI procedure to improve the contrast of the MRI images. Thus, this invention also relates to medical procedures in which spin-polarized xenon.sup.129 gas produced according to the teachings of the invention is utilized.
2. Related Technology
It is recognized that hyperpolarized (i.e., spin-polarized) xenon.sup.129 gas is a significant contrast enhancement agent for use in magnetic resonance imaging (MRI) of human lung and bronchial structures in living humans. Potentially, there is a need for about 10 million such MRI procedures in the United States each year. These procedures could benefit from the improved contrast which would be provided were a medical grade of polarized xenon.sup.129 gas to be readily available. Consumption of polarized xenon.sup.129 gas would be in the range of from one to five grams of the gas for each such MRI procedure. Accordingly, for each facility performing such procedures, a few tens of grams of polarized xenon.sup.129 gas would be required each day.
It has been thought that a potential way to provide spin-polarized xenon.sup.129 gas is to first induce spin-polarization of rubidium (Rb) gas by use of laser pumping, and to exchange spin energy from the Rb gas to xenon gas to provide collision-induced polarization of the xenon gas. After the xenon gas is polarized, the two gases must be separated, and the spin-polarized xenon is then available for use as a contrast medium. However, prior to this invention a number of insurmountable problems have existed with this potential approach. First, because of the residue of Rb gas present in the xenon gas after the two gases are "separated", and which residue of Rb is toxic to human tissues, the spin-polarized xenon gas was not of medical-grade quality and was not usable in human treatment. Secondly, the efficiency with which laser optical pumping of the Rb gas could be effected was so low and the resulting power requirements for the laser equipment was so high (and therefore, costly) that the process could not be economically justified.